When facsimile signals representing graphic information are received at a recorder they contain in addition to the graphic information a signal to the recorder to start scanning line by line across electrosensitive recording paper, and also a series of framing pulses signalling the beginning of each incoming line of information to be recorded. A scanning motor drives a scanning belt carrying masking styli or a drum having a helix curved around it for scanning successive lines of the recording paper. For undistorted recording of each line of the incoming graphic information signal it is essential that each line scan of the paper be synchronous, in phase, with the receipt of the incoming line of graphic information. At the beginning of each graphic information signal is the aforementioned framing pulse. The recorder generates a corresponding pulse at the start of each scan line. For example, as a scanning helix is revolved by the recorder motor a reed switch is actuated at the beginning of each helix line scan so as to generate a recorder pulse. The recorder is synchronized with the incoming signal by comparing the time of occurrence of the recorder pulse and the framing pulse. As shown, for example, in U.S. Pat. No. 2,686,832 the recorder motor is then controlled until the recorder pulse is synchronous with the framing pulse.
The object of the present invention is to provide an improved motor control circuit which more rapidly achieves synchronism, particularly with motors of small torque output.